In right triangle $DEF$, we have $\angle D = 25^\circ$, $\angle E = 90^\circ$, and $EF = 9$.  Find $DE$ to the nearest tenth.  You may use a calculator for this problem.
Solution: We start with a diagram:

[asy]
pair D,EE,F;

EE = (0,0);
F = (8,0);
D = (0,8*Tan(65));
draw(D--EE--F--D);
draw(rightanglemark(F,EE,D,18));
label("$E$",EE,SW);
label("$F$",F,SE);
label("$D$",D,N);
label("$9$",F/2,S);
[/asy]

We seek $DE$, and we have $EF$ and $\angle D$.  We can relate these three with the tangent function: \[\tan D = \frac{EF}{DE},\]so  \[DE = \frac{EF}{\tan D} = \frac{9}{\tan D} \approx \boxed{19.3}.\]